There are three basic methods which are known for transferring energy from a first fluid flow to a second. They are indirect transfer by dynamic machines, direct nonsteady-flow transfer by pressure waves, and direct steady-flow transfer by mixing of the fluid flows.
The indirect nonsteady-flow transfer by dynamic machines may be exemplified by considering a turbo charger where energy is extracted from one flow by a turbine and added to a second flow by a compressor mechanically coupled to the turbine.
Direct nonsteady-flow transfer by pressure wave is a type of energy transfer normally associated with the operation of a pulse jet engine. The energy transfer is accomplished by air which enters the tail pipe of the engine and bodily compresses the air in the combustor of the engine, there being a transfer of energy without significant mixing of the bodies of air.
Direct steady-flow transfer by fluid mixing involves a high energy primary flow and a low energy secondary flow. The two flows are merged or mixed in a common duct where there is a transfer of momentum and a redistribution of the energy of the flows. The flow emerging from the mixing duct has an energy level which is between the levels of the two initial flows.
It is further known to employ apparatus to shape, redirect or otherwise act on the exhaust of a reaction motor to thereby vary certain characteristics of the exhaust. U.S. Pat. Nos. 3,273,654; 3,731,489; 3,981,451 and 4,036,452 disclose apparatus where an entire pivotally mounted assembly may be placed in such an exhaust. It is also known to vary the area of an exhaust nozzle by means of a variable nozzle made up of connected elements. And U.S. Pat. Nos. 3,441,219 and 3,664,455 disclose apparatus comprised of a number of elements each of which is pivotable about an axis parallel to the exhaust flow. And in compressors, it is known to provide variable inlet guide vanes and stator blades. However, none of these prior art devices use vortex generators as energy transfer means.